Off diagonal elements in dashpot elements

Dose any body know how I can introduce off diagonal components of the damping matrix for dashpot elements in Ruaumoko3D. I wonder why it is not as straight forward as that of spring elements.

I presume by off-diagonal elements you want a dashpot to have say, longitudinal (x) forces from transverse (y) velocities?. You can set up dashpots in any of the directions within the member but as in spring elements they are assumed to be directly proportional to the deformations in that direction.

I need for instance longitudinal force resulted from rotational velocity.
needed to model translation and rocking motion of foundation in SSI analysis.
how can I achieve this goal by setting up multiple damper elements?
Thanks